Combustion system with a corona electrode

ABSTRACT

A corona electrode may be used to apply an electric field to a combustion reaction to cause a response in the combustion reaction. The corona electrode may include an ion-ejecting feature having a small radius.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase application under 35U.S.C. 371 of co-pending International Patent Application No.PCT/US2013/048937, entitled “COMBUSTION SYSTEM WITH A CORONA ELECTRODE”,filed Jul. 1, 2013; which application claims the benefit of U.S.Provisional Patent Application No. 61/666,757, entitled “COMBUSTIONSYSTEM WITH A SHARP ELECTRODE”, filed Jun. 29, 2012; and from U.S.Provisional Patent Application No. 61/694,207, entitled “COMBUSTIONSYSTEM WITH A SERRATED ELECTRODE”, filed Aug. 28, 2012, now expired; allof the foregoing applications are incorporated herein by reference intheir entireties.

BACKGROUND

Combustion systems may benefit from applying one or more electricfields, charge, or electrical potential to a combustion reaction.

SUMMARY

Little or no benefit has been heretofore reported regarding theapplication of the electric field(s) to a combustion reaction as afunction of electrode shape. The inventors have determined that theshape of an electrode used to apply an electrical field to a combustionreaction can affect the shape and intensity of the electric field, aswell as its effect on the combustion reaction. Moreover, the inventorshave determined that corona electrodes can eject charges that areincorporated into the combustion reaction, without the necessity ofmaintaining physical contact between the combustion reaction and thecorona electrode. What is needed are electrode shapes that providedesired electric field strength interacting with a combustion reaction.

In researching and developing electrodes for use in applying anelectrical charge to a combustion reaction, the inventors havedetermined that some electrode shapes and materials, in some combustionsystems, are subject to thermal ablation that can reduce theeffectiveness or shorten the life of the electrodes. This isparticularly the case where a sharp or thin (i.e., corona) electrode isused in a burner system that achieves very high temperatures, or insystems in which the electrode is in direct contact with a flame orother kind of combustion reaction.

According to various embodiments, structures are provided that addressthese concerns, and that provide additional benefits, as well.

According to an embodiment, combustion system benefits from the use ofone or more electrodes configured to generate high electric fieldstrength proximate to the surface of the electrode(s). An electrodeconfigured to generate a high electric field strength proximate to itssurface sufficient to eject charges is referred to as a coronaelectrode. Such an electrode can be alternatively referred to as a sharpelectrode, an ionizing electrode, an ion-ejecting electrode, andion-injecting electrode, or, in some contexts, simply an ionizer.

According to an embodiment, an electrode system for a combustionapparatus is provided that includes at least one corona electrodeconfigured for mounting proximate to a combustion reaction. A powersupply is operatively coupled to the corona electrode(s) and to thecombustion reaction zone (e.g., flame). The power supply and the coronaelectrode(s) can be configured to apply an electric field to a regionadjacent to the combustion reaction. The corona electrode can becharacterized as producing an electric field having a maximum magnitudeadjacent to the corona electrode at least double an average electricfield magnitude in the region adjacent to the combustion reaction. Theelectric field and/or charges produced by the corona electrode(s) areconfigured to cause ions to be injected into the combustion reaction,thus providing increased mixing of fuel and oxidizer in the combustionreaction.

According to another embodiment, a combustion system includes a serratedor sawtooth corona electrode. The combustion system includes a fuelburner structure configured to support a combustion reaction. Thecombustion system includes a serrated corona electrode configured toform an electrical relationship with the combustion reaction. Theserrated electrode includes a plurality of sharp projections configuredto at least intermittently eject ions into a dielectric gap between theplurality of projections and the combustion reaction. Each of theplurality of projections is configured to at least intermittently ejections into the dielectric gap responsive to receiving an ion ejectionvoltage from an electrical coupling.

According to an embodiment, a system is provided for applying a chargeor voltage to a combustion reaction. The system includes a power supplyconfigured to output a voltage of 1000 volts or more. The systemincludes one or more electrodes operatively coupled to the power supplyand configured to eject ions into a region proximate to the combustionreaction. The system includes at least one counter electrode configuredto at least intermittently receive or supply current to the combustionreaction responsive to the ions ejected by the one or more electrodes.

According to further embodiments, methods for applying an electric fieldto a combustion reaction are provided, which include supporting at leastone corona electrode proximate to but not contacting a combustionreaction. The corona electrode(s) can be characterized as including oneor more small radius tips or edges. A voltage is applied to the coronaelectrode(s) to cause ion ejection in a high electrical field strengthvolume peripheral to the small radius tip(s) or edge(s) of theelectrode. A response in the combustion reaction is caused responsive tothe application of the electric field strength and ion ejection.

According to another embodiment, a system is provided that includes acorona electrode positioned adjacent to a burner assembly and configuredto form an electrical relationship with a combustion reaction supportedby the burner assembly. A radiation shield is provided, positionedbetween at least a portion of the electrode and the combustion reaction,configured to attenuate or block radiant heat emanating from thecombustion reaction that would otherwise impinge on the electrode.

According to another embodiment, a corona electrode is provided,configured for use in a combustion system

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a combustion system including a corona electrodeconfigured to apply an electric field to a combustion reaction,according to an embodiment.

FIG. 2 is a diagram showing illustrative electric field strength andvoltage between a corona electrode and a dull electrode, according to anembodiment.

FIG. 3 is a diagram of a combustion system including a corona electrodeand a dull electrode, according to an embodiment.

FIG. 4 is a view of a corona electrode assembly including a coronaelectrode configured as a pointed cylinder, according to an embodiment.

FIG. 5 is a view of a corona electrode assembly including a coronaelectrode configured as a blade, according to an embodiment.

FIG. 6 is a view of a corona electrode assembly including a serratedelectrode, according to an embodiment.

FIG. 7 is a view of a corona electrode assembly including a serratedelectrode, according to another embodiment.

FIG. 8 is a flow chart showing a method for applying an electric fieldor voltage to a combustion reaction using a corona electrode, accordingto an embodiment.

FIG. 9 is a view of a corona electrode assembly including a radiationshield configured to protect the electrode from radiant heat, accordingto an embodiment.

FIG. 10 is a view of a corona electrode assembly including a radiationshield configured to protect the electrode from radiant heat, accordingto another embodiment.

FIG. 11 is a view of a corona electrode assembly including aself-sharpening electrode, according to another embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. Other embodiments may be used and/or other changesmay be made without departing from the spirit or scope of thedisclosure.

For brevity, elements disclosed with respect to a system illustrated inone figure may not be disclosed or described in detail with respect tosystems of other figures. Nevertheless, those of skill in the art willrecognize the combinability of many of the features disclosed herein.

When a voltage is applied to an electrode, an electric field is formedaround the electrode. The relative strength of the electric field at anygiven location adjacent to the electrode is inversely related to theradius of the curvature of the electric potential at that location.Thus, a corona electrode, i.e., an electrode with a very small radius atthe point, will generate a large electric field strength near itscurvature relative to a field strength adjacent to other portions of theelectrode.

FIG. 1 is a diagram of a combustion system 101 including a coronaelectrode 102 configured for mounting proximate to a combustion reaction104 such as, e.g., a flame, supported by a burner 112 in a combustionvolume 103, according to an embodiment. The combustion volume 103 can bedefined by furnace walls, boiler walls, a rotary kiln, etc. Suchcombustion volumes 103 are generally separated from work areasaccessible to operating engineers and other persons. A power supply 106is operatively coupled to the corona electrode 102 and to the burner112. The power supply 106 and the corona electrode 102 are configured tocooperate to apply an electric field to a region 108 in the combustionvolume 103 adjacent to the combustion reaction 104, with the magnitudeof the electric field near the corona electrode 102 being at least twicethe average magnitude of the electric field in the region 108 adjacentto the combustion reaction 104.

In other words, a corona electrode 102 can be characterized as anionizing electrode because a small physical radius of at least a portionof the electrode causes high curvature in the electric field, and hencehigh electric field strength E in near proximity to a sharp surface. Thehigh electric field strength is associated with insertion of ions 111from the corona electrode 102 into the dielectric layer, or region, 108upon application of high voltage to the corona electrode 102. Theinserted ions 111 can be referred to as a corona discharge.

According to other embodiments, the combustion system 101 may include aplurality of corona electrodes 102 configured for mounting proximate tothe combustion reaction 104 and operatively coupled to the power supply106, or a plurality of power supplies 106.

FIG. 2 is a graph 201 showing an illustrative variation of electricfield strength E and an illustrative voltage V in the dielectric gap orregion 108 between a corona electrode 102 and the combustion reaction104. The position on the abscissa X is indicative of the distancebetween the corona electrode 102 and the combustion reaction 104(increasing from left to right). The curves shown in FIG. 2 occurresponsive to an electric potential being applied between the coronaelectrode 102 and the combustion reaction 104. The solid curve labeled Ein the graph in FIG. 2 depicts the electric field strength between thecorona electrode 102 and the combustion reaction 104. The maximumelectric field strength occurs immediately adjacent to corona electrode102. The dashed curve labeled V depicts the variation in voltage betweenthe corona electrode 102 and the combustion reaction 104 under the sameapplied electric potential, where V_(MAX) is an electrical potentialapplied to the corona electrode 102 and V_(FLAME) is an electricalpotential (or a calculated potential corresponding to a charge density)of the combustion reaction 104.

Generally, corona electrodes 102 are characterized as having a smallradius feature (which may include a point or a line) that tends toconcentrate an applied voltage into a relatively small volume peripheralto the small radius feature. Some example electrode shapes used by theinventors include needle, blade, saw-tooth, and thin wire. By contrast,dull electrodes 110 are defined as having a large effective surface withlittle or no concentration of applied voltage, such that the electricfield magnitude adjacent to them is low, relative to the field strengthat the tip or edge of a corona electrode 102 energized at the samepotential. For the purposes of this disclosure, the highest fieldmagnitude adjacent to a dull electrode 110 is less than twice theaverage electric field magnitude between the dull electrode 110 and thecooperating corona electrode or electrodes 102.

Typically, in known systems that employ corona discharge, a coronaelectrode 102 is used in concert with a dull electrode 110 (alsoreferred to as a counter electrode) that carries different electricalpotential, such as ground potential or an opposing potential. Thecounter electrode 110 is dull so as to attract the ions 111 generated bythe corona electrode 102 without generating ions 111 of its own. Asshown in FIG. 1, the burner 112 is coupled to ground and functions as adull electrode 110.

However, according to other embodiments, the combustion reaction 104itself can be considered to act as the dull electrode 110 because itsfluid nature responds to charge concentrations in a surroundingdielectric (e.g. air) region by assuming a shape that distributes thecharge concentration over a larger area of the combustion reaction 104,the fluid response acting to substantially prevent ion ejection from thecombustion reaction 104 to the dielectric.

According to other embodiments, a counter electrode 110 (not shown) canbe provided to draw the emitted ions away from the corona electrode 102.The combination of the corona electrode 102 and the counter electrode110 can create an ionic wind that causes ejected ions 111 to streamtoward and combine with the combustion reaction 104.

Generally, a dull electrode 110 includes only large radius features thatdo not significantly concentrate an applied voltage into a small volumeperipheral to the electrode. Dull electrodes 110 generally are notconsidered charge-ejecting or ionization-inducing bodies, whereas coronaelectrodes 102 are regarded as ionizing or charge ejecting bodies thatlaunch charged particles into the surrounding volume when exposed torelatively high voltage. Many known devices take advantage of thisproperty. Examples include electrostatic precipitators, which typicallyuse corona electrodes 102 that deposit charges onto airborne particlesthat are then trapped by electrical attraction to a ground or counterelectrode 110, which is typically a dull electrode 110.

In the combustion system of FIG. 1, the electric field in the vicinityof the corona electrode 102, the cumulative particle charge emitted bythe corona electrode 102, and/or the kinetic energy of the chargedparticles emitted by the corona electrode 102 affect the motion ofparticles in the combustion reaction 104. One such effect may be tocause increased mixing of the fuel and oxidizer components of thecombustion reaction 104. Increased mixing of the fuel and oxidizer inthe combustion reaction 104 produces several effects on combustionreaction 104, which can occur singly or in combination. The increasedmixing can increase a reaction rate of the combustion reaction 104,and/or can increase fuel and air contact area within the combustionreaction 104. Increased mixing of fuel and air can cause a decrease ofthe combustion reaction temperature, a decrease of an evolution ofoxides of nitrogen (NOx) and/or carbon monoxide (CO) in the combustionreaction 104, an increase of stability of the combustion reaction 104,and/or a decrease of a chance of combustion reaction blow-out. Increasedfuel-air mixing can cause an increase in emissivity of the combustionreaction 104, or a decrease in the size (such as volume) of thecombustion reaction 104 for a given fuel flow rate.

The voltage applied to the corona electrode(s) 102 by the power supply106 can be a substantially constant DC voltage, a time-varying voltage,or a DC voltage with a superimposed time-varying voltage. A time-varyingvoltage can have a periodic voltage waveform with a frequency in therange from 50 to 10,000 Hertz, for example. According to someembodiments, the time-varying voltage can have a periodic voltagewaveform with a frequency in the range from 200 to 800 Hertz. N.B. Thewaveform of the time-varying voltage can be any of a number of shapes,including a square waveform, sine waveform, triangular waveform,truncated triangular waveform, sawtooth waveform, logarithmic waveform,or exponential waveform, for example. Additionally or alternatively, thewaveform shape can include a combination of square waveform, sinewaveform, triangular waveform, truncated triangular waveform, sawtoothwaveform, logarithmic waveform, or exponential waveform. The amplitudeof the time-varying voltage can be in the range ±1,000 volts to ±115,000volts, for example. According to some embodiments, the time-varyingvoltage can have an amplitude in the range ±8,000 volts to ±40,000volts. The magnitude of the electric field in region 108 can be in therange from 0.3 kV/m (kilovolts per meter) to 1,000 kV/m, for example.According to some embodiments, the electric field strength in the region108 can be between 80 kV/m and 400 kV/m.

Electrically conductive surfaces energized to high positive or negativevoltages may exhibit the phenomenon known as corona discharge. Coronadischarge typically occurs due to ionization of an adjacent dielectricmedium.

The conditions under which corona discharge occurs can be calculatedwith a mathematical equation known as Peek's Law.

For example, one form of Peek's Law gives e_(v), the minimum voltagenecessary for corona discharge to occur (the “corona inception voltage”in kilovolts) between two wires according to the formula:

$e_{v} = {m_{v}g_{v}\delta_{r}{\ln \left( \frac{S}{r} \right)}}$

Where m_(v) is an irregularity factor depending on the condition of thewires, typically ranging between 0.9 and 1.0, and

g_(v) is the visual critical potential gradient, a function of airdensity δ (which varies with air temperature and pressure) and theradius r of the wires, and

S is the distance between the wires.

According to Peek's Law, the smaller the radius of the wires, the lessvoltage is needed to initiate corona discharge. In general, coronadischarge is more likely to occur from sharply angled or pointedelectrodes such as corona electrode 102 than from dull electrodes suchas dull electrode 110 (shown in FIG. 1), because the electric fieldgradient has its greatest magnitude close to the corona electrode 102.In the Peek's Law equation, a corona electrode 102 has a small effectivevalue of r, and hence a lower corona inception voltage than a dullelectrode 110 having a larger effective r.

Applying Peek's Law, the corona inception voltage for an apparatus suchas that shown in FIG. 1 can be determined, and the output of the powersupply 106 (shown in FIG. 1) can be adjusted so that the electric fieldstrength near the corona electrode 102 is at least equal to the coronainception voltage. Such a condition causes corona discharge. Accordingto an embodiment, the electrode is considered sufficiently sharp if themaximum electric field strength near the corona electrode 102 is atleast double the average electric field strength E between the coronaelectrode 102 and a dull electrode 110 or between the corona electrode102 and the combustion reaction 104, indicated by the horizontal linelabeled E in FIG. 2.

Since the combustion reaction 104 generates many charged particles thatare capable of supporting the flow of electric current, the surface of aflame 104 can be treated as a substantially equipotential conductivesurface that cooperates with the at least one corona electrode 102 toproduce the electric field. In other words, the combustion reaction 104can be considered to be the counter electrode 110.

In an embodiment, at least one second corona electrode 102 is included,configured for mounting proximate to the combustion reaction 104 andcooperating with the first corona electrode(s) 102 to produce theelectric field.

The burner 112 can act as a second electrode 110 and can be inelectrical continuity with a conductive surface of the combustionreaction 104. The burner 112 can be configured to define a countervoltage to cooperate with the corona electrode(s) 102 to produce theelectric field.

According to an embodiment, the burner 112 also functions as the dullelectrode 110, which is operatively coupled to the power supply 106.Likewise, where the combustion reaction 104 functions as the dullelectrode 110, the countercharge can be applied via the burner 112, fromwhich the charge is carried by the fuel stream into the combustionreaction 104. According to another embodiment, the countercharge isapplied to the conduit that carries the fuel to the burner 112.

The electric potential of the burner 112 or fuel conduit can be heldsubstantially at ground voltage. Alternatively, the burner 112 can begalvanically isolated from ground and from power supplies 106 other thanthe corona electrode 102, such that the burner 112 is floating.

FIG. 3 is a diagram showing a combustion system 301 including a coronaelectrode 102 and a dull electrode 110 proximate to the combustionreaction 104 supported by a burner 112, according to an embodiment. Apower supply 106 is operatively coupled between the dull electrode 110and the corona electrode 102 to provide a voltage difference to producethe electric field. Because the dull electrode 110 lacks thesmall-radius features found on corona electrode 102, it does notsignificantly concentrate an applied voltage into a small volumeadjacent to the electrode and thus does not tend to eject charge into orinduce ionization of the surrounding dielectric medium.

The dull electrode 110 is configured so that the electric field adjacentto it is about equal to or less than the average electric fieldmagnitude in the region between electrodes 102 and 110, according to anembodiment.

According to an embodiment, the dull electrode 110 can be configured inthe shape of a toroid or torus, as shown. The dull electrode 110 isoperatively coupled to the power supply 106. The dull electrode 110 canbe held substantially at ground potential, or can be configured to bedriven to an instantaneous voltage substantially the same as theinstantaneous voltage applied to the corona electrode 102. The dullelectrode 110 can be configured to be galvanically isolated from groundand from other electrical potentials.

FIG. 4 is a view of a corona electrode assembly 401 including a coronaelectrode 102 configured as a pointed cylinder, according to anembodiment. The corona electrode 102 includes a cylindrical taper 402 toa tip 404 having a radius of 0.1 inch or less. The corona electrode 102and/or the assembly 401 also includes an electrical coupling 406, whichmay include an electrical lug for attachment of a wire or otherconductor. The corona electrode 102 and/or assembly 401 can includeelectrical insulation 408 to substantially prevent current flow betweenthe corona electrode 102 and a surface or apparatus it is mounted to. Anelectrically-isolated mounting bracket 410 can include a flangeconfigured to mount the corona electrode 102 to a mounting surface 114(shown in FIG. 1), which can include a burner body, a boiler, a furnacewall or other structure.

FIG. 5 is a diagram of a corona electrode assembly 501 including acorona electrode 102 configured as a conductive blade, according to anembodiment. The corona electrode 102 includes a taper 502 to an edge 504having a radius of 0.1 inch or less, for example. An electrical coupling406 is configured as a tapped hole in the corona electrode 102 forreceiving an electrical connection (not shown). An electrically-isolatedmounting bracket 410 can include a clamp configured to compresselectrical insulation 408 against the electrode 102 body. The mountingbracket 410 can include a mounting point 506 for mounting the assembly501 to a burner body, a boiler, a furnace wall or other structure (notshown).

The corona electrode 102 can be configured to operate in a relativelyhigh temperature environment, in or adjacent to a combustion reaction104. The corona electrode 102 can be constructed from a conductivematerial capable of withstanding a relatively high temperaturecorresponding to a combustion volume. For example, the corona electrode102 can be made from iron, steel, platinum, palladium, tungsten, ahigh-temperature alloy, compressed carbon, silicon carbide, or aconductive ceramic. In an embodiment, the corona electrode 102 is madeof stainless steel. Optionally, the corona electrode 102 is activelycooled, for example by circulating water or another cooling fluidthrough coolant passages (not shown) in the body of the corona electrode102.

FIG. 6 is a diagram of a combustion system 600 including a coronaelectrode (e.g., 102, shown in FIG. 1) structured as a serrated coronaelectrode 606 (also referred to as “serrated electrode”), according toanother embodiment. The system 600 includes a fuel burner structure 112configured to support a combustion reaction 104. The serrated electrode606 is configured to form an electrical relationship with the combustionreaction 104. The serrated electrode 606 includes a plurality ofprojections 608 a, 608 b, each configured to generate an increasedelectric field strength at their respective tips, substantially asdescribed above with reference to the corona electrodes 102 of FIGS.1-5, and thus at least intermittently eject ions 111 into a dielectricgap 108 between the plurality of projections 608 a, 608 b and thecombustion reaction 104. The plurality of projections 608 a, 608 b areconfigured to at least intermittently eject the ions 111 responsive toreceiving an ion ejection voltage from an electrical coupling 406.

According to an embodiment, the dielectric gap 112 between the pluralityof projections 608 a, 608 b and the combustion reaction 104 includesair. Additionally or alternatively, the dielectric gap 112 can includeflue gas.

The system 600 includes the electrical coupling 406 to the serratedelectrode 106. The electrical coupling 406 includes a current channeloperatively coupled to the power supply 106 (not shown in FIG. 6),according to an embodiment.

The electrical relationship between the serrated electrode 106 and thecombustion reaction 104 includes an addition of charge to the combustionreaction 104. Additionally or alternatively, the electrical relationshipbetween the serrated electrode 106 and the combustion reaction 104 caninclude the application of a voltage to the combustion reaction 104.

According to an embodiment, the system 600 includes a fuel source 616configured to provide a fuel stream 618 to support the combustionreaction 104.

The system 600 includes a dull electrode 110. The dull electrode 110 isconfigured to be maintained in at least an intermittent capacitiverelationship to the ejected ions 111. Additionally or alternatively, thedull electrode 110 can be configured to be maintained in at least anintermittent capacitive relationship to the plurality of projections 608a, 608 b, to the serrated electrode 106, and/or to the electricalcoupling 406.

The system 600 includes an electrode-mounting surface 114. Theelectrode-mounting surface 114 is configured to mechanically couple theserrated electrode 606 to the other elements of the burner system 600.According to an embodiment, the mounting surface 114 is electricallyinsulated from the serrated electrode 606, as described with referenceto FIG. 4. According to other embodiments, the electrode-mountingsurface 114 forms a portion of the electrical coupling 406. Additionallyor alternatively, the electrical coupling 406 can form a portion of theelectrode-mounting surface 114. According to another embodiment, theelectrode-mounting surface 114 and the electrical coupling 406 aresubstantially congruent. Additionally or alternatively, theelectrode-mounting surface 114 and the electrical coupling 406 can be inelectrical continuity with one another.

According to an embodiment, the electrode-mounting surface 114 includesa clamp configured to hold the serrated electrode 606 in a substantiallyconstant position relative to the fuel burner structure 112.Additionally or alternatively, the clamp can be configured to hold theserrated electrode 606 in one or more positions relative to the fuelburner structure 112.

According to another embodiment, the electrode-mounting surface 114 canbe configured to move the serrated electrode 606 to a time-varyingplurality of positions relative to the fuel burner structure 112. Thetime-varying plurality of positions corresponds to one or more serratedelectrode 606 loading actuation movements. The time-varying plurality ofpositions corresponds to vibration, translation along one or more axes,rotation about one or more axes, and/or yaw relative to one or moreaxes. Additionally or alternatively, the time-varying plurality ofpositions correspond to a heat-cycling movement of the serratedelectrode 606 relative to the fuel burner structure 112 and thecombustion reaction 104.

In an embodiment of the system 600, the serrated electrode 606 includesa sawblade originally configured to fit a powered saw body or a hand sawbody. For example, the serrated electrode 606 can be at least derivedfrom a sawblade configured to fit a powered saw body or a hand saw body.

According to an embodiment, the serrated electrode 606 includes anelectrode body 624 operatively coupled to the plurality of projections608 a, 608 b. According to another embodiment, the serrated electrode606 includes the electrode body 624 operatively coupled to a pluralityof corona electrode portions including the plurality of projections 608a, 608 b. Additionally or alternatively, the electrode body 624 caninclude the plurality of corona electrode portions including theplurality of projections 608 a, 608 b.

In an embodiment, the combustion reaction 104 includes a flame.

FIG. 7 is a diagram of a system 700 for applying charge or voltage to acombustion reaction 104, according to an embodiment. The system 700includes a power supply 106 configured to output a voltage of 1000 voltsor more. The system 700 also includes one or more serrated electrodes606 operatively coupled to the power supply 106. The one or moreserrated electrodes 606 are configured to eject ions 111 into a region108 proximate to a combustion reaction 104. The system 700 includes acounter electrode 110 configured to at least intermittently receivecurrent responsive to the ions 111 ejected (or emitted) by the serratedelectrode 606. The counter electrode 110 is configured to at leastintermittently supply current to the combustion reaction 104 responsiveto the ions 111 ejected by the serrated electrode 606.

The region 108 proximate to the combustion reaction 104 can be adielectric gap. The region 108 can, for example, include air or fluegas.

According to an embodiment, the system 700 includes a fuel burnerstructure 112 configured to support the combustion reaction 104.

According to an embodiment, the receipt or supply of ionic current bythe counter electrode 110 can be selected to anchor the combustionreaction 104 proximate to the counter electrode 110. The counterelectrode 110 can also be electrically coupled to ground.

According to an embodiment, the system 700 includes a conductive fuelnozzle tip 706 electrically coupled to ground. For example, the counterelectrode 110 can include a toric structure held circumferential to thefuel stream 618 output by the fuel source 616 (shown in FIG. 6).

FIG. 8 is a flowchart showing a method 801 for applying an electricfield or voltage to a combustion reaction, according to an embodiment.In step 802 a corona electrode is supported proximate to a combustionreaction. The corona electrode may includes a small radius tip or edge,or, alternatively, includes a plurality of tips, as in a serratedelectrode. In step 806, a voltage is applied to the corona electrode tocause ion ejection in a voltage concentration volume peripheral to thesmall radius tip(s) or edge. In step 808, responsive to the applicationof the voltage and ion ejection, a response is caused in the combustionreaction. According to an embodiment, step 802 includes supporting thecorona electrode proximate to but not contacting the combustionreaction.

In embodiments that employ one or more serrated electrodes, eachserrated electrode includes an electrode body and a plurality ofprojections coupled to or intrinsic to the electrode body. Each of theplurality of projections is shaped to cause corona ejection of ionsresponsive to the applied voltage.

According to an embodiment, at least a portion of the ejected ionstravel across the dielectric gap to the combustion reaction to chargethe combustion reaction. The dielectric gap can include air and/or caninclude flue gas.

According to an embodiment, the method 801 includes step 804, whichincludes supporting a second electrode proximate to or contacting thecombustion reaction. Supporting a second electrode may includesupporting a second corona electrode proximate to but not contacting thecombustion reaction. Alternatively, supporting the second electrodeproximate to or contacting the combustion reaction may includesupporting at least one dull electrode to cooperate with the at leastone corona electrode to produce an electric field.

In step 806, according to an embodiment, applying the voltage to thecorona electrode results in an electric field magnitude adjacent to adull electrode that is no larger than twice the average electric fieldmagnitude between the electrodes, while an electric field magnitudeadjacent to the corona electrode is at least twice the average electricfield magnitude between the electrodes.

Supporting the second electrode proximate to or contacting thecombustion reaction can include supporting a toroid or torus. The method801 can optionally include driving the second electrode to aninstantaneous voltage substantially the same as the instantaneousvoltage applied to the corona electrode. Alternatively, the secondelectrode can be held substantially at voltage ground. Alternatively,the second electrode can be isolated from ground and from voltages otherthan a voltage received from the corona electrode.

According to another embodiment, the method includes moving the serratedelectrode to a time-varying plurality of positions relative to the fuelburner structure.

According to an embodiment, the corona electrode includes a cylindricaltaper to a tip having a radius of 0.1 inch or less. This radius ispreferably less than 0.004″ for most applications. According to anotherembodiment, the corona electrode includes a conductive blade having ataper to an edge having a radius of 0.1 inch or less. Alternatively, thetip or edge can be larger than 0.1-inch radius, especially underconditions of higher voltage or appropriate counter electrode/combustionreaction geometry is maintained to conform with Peek's Law.

Applying a voltage to the corona electrode in step 806 can includeoperating a power supply to apply a high voltage to the coronaelectrode(s). Applying the voltage to the at least one corona electrodecan include applying an electric field to a region adjacent to thecombustion reaction, the electric field having a maximum magnitude inthe voltage concentration volume peripheral to the small radius tip oredge at least double an average electric field magnitude in the regionadjacent to the combustion reaction.

Applying a voltage to the at least one corona electrode in step 806 caninclude applying a substantially constant voltage to the at least onecorona electrode. Alternatively, applying a voltage to the at least onecorona electrode in step 806 can include applying a time-varying voltageto the at least one corona electrode.

Applying the time-varying voltage can include applying a periodicvoltage waveform having a 50 to 10,000 Hertz frequency. For example,applying the time-varying voltage can include applying a periodicvoltage waveform having a 200 to 800 Hertz frequency. Applying thetime-varying voltage can include applying a square waveform, sinewaveform, triangular waveform, truncated triangular waveform, sawtoothwaveform, logarithmic waveform, or exponential waveform. Applying thetime-varying voltage can include applying a waveform having ±1000 voltto ±115,000 volt amplitude. For example, applying the time-varyingvoltage can include applying a waveform having ±8000 volt to ±40,000volt amplitude. Applying the voltage to the at least one coronaelectrode in step 806 can include applying an average electric fieldmagnitude in the region adjacent to the combustion reaction between 0.3kV/m to 1000 kV/m. For example, applying the voltage to the at least onecorona electrode can include applying an average electric fieldmagnitude in the region adjacent to the combustion reaction between 80kV/m to 400 kV/m. Applying the voltage to the at least one coronaelectrode can include applying an average electric field magnitudesufficient to meet a corona inception voltage according to Peek's law.

Referring to step 808, causing a response in the combustion reactionincludes causing a visible response in the flame, according to anembodiment. Additionally or alternatively, causing a response in thecombustion reaction can include causing increased mixing of fuel andoxidizer in the combustion reaction. Causing the increased mixing offuel and oxidizer can increase a rate of combustion. Additionally oralternatively, causing the increased mixing of fuel and oxidizer canincrease fuel and air contact in the combustion reaction. Additionallyor alternatively, causing the increased mixing of fuel and oxidizer candecrease a combustion reaction temperature. Additionally oralternatively, causing the increased mixing of fuel and oxidizer candecrease an evolution of oxides of nitrogen (NOx) by the combustionreaction. Additionally or alternatively, causing the increased mixing offuel and oxidizer may decrease an evolution of carbon monoxide (CO) bythe combustion reaction. Causing the increased mixing of fuel andoxidizer may increase flame stability and/or decrease a chance of flameblow-out. Additionally or alternatively, causing the increased mixing offuel and oxidizer can increase combustion reaction emissivity.Additionally or alternatively, causing the increased mixing of fuel andoxidizer can decrease combustion reaction size for a given fuel flowrate.

According to an embodiment, the method 801 includes causing a conductivesurface of the combustion reaction to form a substantially equipotentialsurface that cooperates with the corona electrode(s) to produce anelectric field between the corona electrode(s) and the combustionreaction (not shown). Causing the conductive surface of the combustionreaction to form a substantially equipotential surface includes applyinga voltage condition to a burner in electrical continuity with thecombustion reaction. Applying a voltage condition to the burner includesoperating a power supply that also applies the voltage to the at leastone corona electrode. Additionally or alternatively, applying a voltagecondition to the burner can include holding the burner substantially atvoltage ground. Applying a voltage condition to the burner can includeisolating the burner from ground and from voltage sources other than thecorona electrode such that the burner is electrically floating.

One problem that the inventors have identified is the potential forthermal ablation of electrodes employed in applying a charge to acombustion reaction. Depending on the particular circumstances andconfiguration, the tip of an electrode can be heated by the combustionreaction to a point that it undergoes gradual sublimation, as moleculesof the material of the electrode are gasified and dispersed.Particularly in cases where the electrode has a relatively sharp tip,the mass of the electrode at the point may not be sufficient to conductheat away from the tip well enough to prevent overheating at the tip. Asa result, the tip ablates and becomes more rounded, reducing theefficiency of the electrode.

In contrast to many other electrode designs, a corona electrode need notmake contact with a combustion reaction, but can be positioned somedistance from the reaction, thus reducing the heat to which it issubjected. On the other hand, because a corona electrode has arelatively sharp tip or edge, it is more susceptible to overheating.

Turning now to FIG. 9, a system 900 is shown, according to anembodiment. In most respects, the system 900 is substantially similar tothe system 100 of FIG. 1, having, for example, a burner 112 configuredto support a combustion reaction 104, and a corona electrode 102configured to eject ions 111 toward the reaction 104. For brevity, otherelements of the system that are previously described, or well known inthe art are not shown.

System 900 includes a radiation shield 902 supported by a bracket 904 ina position directly between the electrode 102 and the combustionreaction 104. Heat radiated by the combustion reaction 104 isintercepted or reduced by the radiation shield 902 such that thetemperature proximate to sharp (ion ejecting) features of the coronaelectrode 102 is reduced. Since a large majority of the heat energyapplied to the corona electrode 102 is in the form of thermal radiation,and thermal radiation is transmitted along a line-of-sight, theradiation shield 902 prevents radiant heat from the combustion reaction104 from impinging on at least the tip of the corona electrode 102. Itwas found by the inventors that high temperature may be associated witha reduction in ion ejection rate by a corona electrode 102 in proximityto a combustion reaction 104. The radiation shield 902 at leastpartially ameliorates this effect.

The bracket 904 can be electrically conductive, semi-conductive, orinsulating. In an embodiment, bracket 904 is formed at least partly froman electrical insulator such as alumina. The radiation shield 902 ismaintained at a floating electrical potential different from theelectrical potential of the corona electrode 102. In another embodimentthe radiation shield 902 may be made of a non-conductive material suchas a ceramic. For example, alumina is a suitable non-conductive materialchoice in some embodiments.

The radiation shield 902 can be electrically conductive,semi-conductive, or insulating.

In an embodiment, the radiation shield 902 floats or is driven to anelectrical potential between the electrical potential of the coronaelectrode 102 and the electrical potential of the combustion reaction104. In another embodiment, the radiation shield 902 is driven to thesame potential as the corona electrode 102. In such a case, one or morecounter electrodes 110 can be disposed to cause the corona electrode 102to emit ions 111. For example, the counter electrode(s) 110 can bedisposed beside the radiation shield 902 to cause ions 111 emitted bythe corona electrode 102 to pass around the radiation shield 902. Inanother example, the counter electrode(s) 110 can be disposed to causethe corona electrode 102 to emit ions 111 in a direction different thana line-of-sight between the combustion reaction 104 and the coronaelectrode 102.

In an embodiment, the radiation shield 902 is configured to not preventejected ions 111 from traveling in the direction of the combustionreaction 104. For example, as described above, the radiation shield 902can be disposed in a direction that is different than an ion streamingdirection. In another embodiment, the radiation shield 902 is formedfrom a screen or includes holes that allow ejected ions 111 to travelfrom the corona electrode 102 and through the radiation shield 902 tothe combustion reaction 104.

In the example of FIG. 9, the radiation shield 902 is sized andpositioned to protect primarily the tip and front portion of the coronaelectrode 102 from radiant heat, which constitute the most vulnerableportions of the corona electrode 102. The radiation shield 902 can bemade larger to protect more of the corona electrode 102, but will tendto block portions of the ions 111 if made too large. Accordingly, theshield is preferably no larger than necessary to prevent directtransmission of radiant heat to the corona electrode 102.

According to various embodiments, the size, shape, optical transparency(e.g., a portion of the radiation shield 902 that is perforated by holesformed therethrough), and position of the radiation shield 902 areselected to protect more or less of the corona electrode 102, accordingto the heat-tolerance of the corona electrode 102.

The bracket 904 can be mounted directly to the corona electrode 102, asshown in FIG. 9, or it can be coupled separately, according to the needsof a particular system.

FIG. 10 is a diagram of a system 1000, according to an embodiment. TheSystem 1000 is substantially similar to the system 600 of FIG. 6,having, for example, a burner 112 configured to support a combustionreaction 104, and a serrated electrode 606 configured to eject ions 111toward the reaction 104. The system 1000 also includes a radiationshield 902 supported by a bracket 904 in a position directly between theserrated electrode 606 and the combustion reaction 104. The radiationshield 902 of the system 1000 functions substantially identically to theradiation shield 902 of the system 900, but is shaped to protect theserrated electrode 606 from the radiant heat of the combustion reaction104. As with the radiation shield 902 of the system 900, the radiationshield 902 is coupled by the bracket 904 directly to the electrode 606.However, this is merely illustrative, and can be configured in a mannerconvenient to the particular system configuration.

FIG. 11 is a diagrammatic view of a system 1100, according to anembodiment. The system 1100 includes a burner 112 configured to supporta combustion reaction 104. The system 1100 also includes a coronaelectrode 1102. The corona electrode 1102 includes a core 1106, asupport body 1108, and a connector 1109 configured to receive anelectrical connection to a power supply (not shown).

A forward end of a corona electrode core 1106 extends slightly beyond aforward end of a support body 1108. Ablation of the core 1106 and thesupport body 1108 tends to result in and sustain a generally sharp shapeon the forward end of the corona electrode 1102. A radius can besubstantially equal to a radius taken in a plane that lies perpendicularto a longitudinal axis of the corona electrode 1102. The core 1106 has aradius selected to be appropriate for the tip radius of a coronaelectrode 102 (shown in FIG. 1), as previously described.

The core 1106 is formulated to have a greater resistance to heat andablation than the support body 1108, and therefore tends to ablate moreslowly than the support body 1108. Additionally, the support body 1108protects the core 1106 from ablation except at the tip, as ablation ofthe support body 1108 exposes the forward end of the core 1106. As thecorona electrode 1102 ablates, the support body 1108 protects areas ofcore 1106 covered thereby, and the greater ablation resistance of thecore 1106 causes the core 1106 to ablate more slowly than the supportbody 1108. The geometry and material properties of the core 1106 and thesupport body 1108 cause the corona electrode 1102 to “self-sharpen” suchthat the tip radius does not increase, but remains consistent.

The core 1106 can be made of a relatively hard, non-reactive, and/orhigh melting point material and the support body 1108 can be made of arelatively soft, reactive, and/or lower melting point material. In oneexample, the core 1106 is carbon steel and the support body 1108 is madeof soft iron. In this example, a self-sharpening characteristic of thecorona electrode 102 is provided primarily by a difference hardnessbetween the core 1106 and support body 1108 materials. In anotherexample, the core 1106 is made of platinum and the support body 1108 ismade of tungsten. In this example, the self-sharpening characteristic ofthe corona electrode 102 is provided primarily by a difference inreactivity between the core 1106 and support body 1108 materials. Othercombinations of core 1106 and support body 1108 materials arecontemplated and fall within the scope of the claims.

In the example of FIG. 11, the system 1100 includes an electrodeadvancement mechanism 1104 configured to advance the electrode 1102toward the combustion reaction 104 as the electrode becomes shorter dueto ablation. The electrode advancement mechanism 1104 includes a steppermotor 1110 controlled by an advancement circuit and coupled toadvancement rollers 1112. The stepper motor 1110 is controllable toextend the electrode 1102 by small and precise increments. An electrodeadvance controller 1114 contains a non-transitory computer-readablemedium carrying computer executable instructions to (optionally) sensean electrode 1102 position and advance or retract the position of theelectrode 1102.

In operation, as the electrode 1102 shortens due to ablation, a sensor(not shown) configured to detect the forward end of the electrodeprovides a signal to the electrode advancement mechanism 1104, whichadvances the electrode toward the combustion reaction 104, therebymaintaining the position of the forward end of the electrode, relativeto the combustion reaction 104. Thus, the length of the portion of thecore 1106 that extends from the support body 1108 remains substantiallyconstant as the electrode 1102 ablates. In an embodiment, the sensor caninclude a current or voltage sensor operatively coupled to the coronaelectrode 1102. In another embodiment, no sensor is used. The electrode1102 is fed forward at a predetermined rate or is repositioned manually.In a manual embodiment, the electrode advance controller includes ahuman interface configured to receive a control input from an operatingengineer. In another embodiment, the electrode 1102 is held in a fixedposition, and the nominal position of the core material 1106 is allowedto recede between scheduled service or replacement.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments are contemplated. The various aspects andembodiments disclosed herein are for purposes of illustration and arenot intended to be limiting, with the true scope and spirit beingindicated by the following claims.

1. An electrode system for a combustion apparatus, comprising: at leastone corona electrode configured for mounting proximate to a combustionreaction; and a power supply operatively coupled to the at least onecorona electrode; wherein the power supply and the at least one coronaelectrode are configured to apply an electric field to a region adjacentto the combustion reaction.
 2. The electrode system for a combustionapparatus of claim 1, wherein the electric field strength has a maximummagnitude adjacent to the corona electrode at least double an averageelectric field strength in the region adjacent to the combustionreaction. 3.-4. (canceled)
 5. The electrode system for a combustionapparatus of claim 1, wherein the power supply is configured to apply asubstantially constant electrical potential to the at least one coronaelectrode. 6.-13. (canceled)
 14. The electrode system for a combustionapparatus of claim 1, wherein the power supply and the at least onecorona electrode are configured to cause an average electric fieldstrength sufficient to meet a corona inception voltage according toPeek's law. 15.-16. (canceled)
 17. The electrode system for a combustionapparatus of claim 22, further comprising: a burner configured tosupport the combustion reaction; wherein the burner further comprisesthe dull electrode and is configured for electrical continuity with aconductive surface of the combustion reaction and to define a countervoltage to cooperate with the at least one corona electrode to producethe electric field. 18.-21. (canceled)
 22. The electrode system for acombustion apparatus of claim 1, further comprising: at least one dullelectrode configured to cooperate with the at least one corona electrodeto produce the electric field. 23.-24. (canceled)
 25. The electrodesystem for a combustion apparatus of claim 22, wherein the dullelectrode includes a toroid or torus.
 26. (canceled)
 27. The electrodesystem for a combustion apparatus of claim 22, wherein the dullelectrode is operatively coupled to the power supply to be driven to aninstantaneous electrical potential different from the instantaneouselectrical potential of the corona electrode.
 28. The electrode systemfor a combustion apparatus of claim 22, wherein the dull electrode isconfigured to be held substantially at ground potential.
 29. Theelectrode system for a combustion apparatus of claim 22, wherein thedull electrode is configured to be galvanically isolated from ground andfrom other electrical potentials.
 30. The electrode system for acombustion apparatus of claim 1, wherein the corona electrode includes ataper to a tip having a radius of 0.1 inch or less.
 31. (canceled)
 32. Amethod for applying an electric field or voltage to a combustionreaction, comprising: supporting at least one corona electrode proximateto or contacting a combustion reaction, the at least one coronaelectrode including a tip or edge of small radius; causing ion ejectionin an electrical field concentration volume peripheral to the tip oredge by applying an electrical potential to the at least one coronaelectrode; and responsive to the application of the electrical potentialand ion ejection, causing a response in the combustion reaction.
 33. Themethod for applying an electric field to a combustion reaction of claim32, wherein supporting at least one corona electrode proximate to thecombustion reaction includes supporting the at least one coronaelectrode proximate to but not contacting the combustion reaction.34.-35. (canceled)
 36. The method for applying an electric field orvoltage to a combustion reaction of claim 32, further comprisingsupporting at least one dull electrode proximate to or contacting thecombustion reaction to cooperate with the at least one corona electrodeto produce an electric field. 37.-38. (canceled)
 39. The method forapplying an electric field or an electrical potential to a combustionreaction of claim 32, wherein supporting the dull electrode proximate toor contacting the combustion reaction includes supporting a toroid ortorus.
 40. The method for applying an electric field or an electricalpotential to a combustion reaction of claim 34, further comprising:driving the dull electrode to an instantaneous voltage substantially thesame as the instantaneous voltage applied to the corona electrode. 41.The method for applying an electric field or voltage to a combustionreaction of claim 34, further comprising: holding the dull electrodesubstantially at ground potential.
 42. The method for applying anelectric field or voltage to a combustion reaction of claim 34, furthercomprising: isolating the dull electrode from ground and from electricalpotentials other than a potential received from the corona electrode.43. The method for applying an electric field or voltage to a combustionreaction of claim 32, wherein supporting at least one corona electrodeproximate to but not contacting the combustion reaction includessupporting a corona electrode including a taper to a tip having a radiusof 0.1 inch or less. 44.-45. (canceled)
 46. The method for applying anelectric field or voltage to a combustion reaction of claim 32, whereinapplying the electrical potential to the at least one corona electrodeincludes applying an electric field to a region adjacent to thecombustion reaction, the electric field strength having a maximummagnitude in the voltage concentration volume peripheral to the smallradius tip or edge at least double an average electric field strength inthe region adjacent to the combustion reaction.
 47. (canceled)
 48. Themethod for applying an electric field or voltage to a combustionreaction of claim 32, wherein applying the electrical potential to theat least one corona electrode includes applying a periodic voltage tothe at least one corona electrode. 49.-53. (canceled)
 54. The method forapplying an electric field or an electrical potential to a combustionreaction of claim 32, wherein applying the voltage to the at least onecorona electrode includes applying an average electric field strength inthe region adjacent to the combustion reaction between 0.3 kV/m to 1000kV/m.
 55. (canceled)
 56. The method for applying an electric field or anelectrical potential to a combustion reaction of claim 32, whereinapplying the electrical potential to the at least one corona electrodeincludes applying an average electric field strength sufficient to meeta corona inception voltage according to Peek's law. 57.-60. (canceled)61. The method for applying an electric field or an electrical potentialto a combustion reaction of claim 32, further comprising providing aburner in electrical continuity with the combustion reaction, wherein aconductive stoichiometric surface of the combustion reaction forms asubstantially equipotential surface in electrical continuity with theburner; and further comprising applying a voltage condition to theburner.
 62. The method for applying an electric field or an electricalpotential to a combustion reaction of claim 61, wherein applying anelectrical potential condition to the burner includes operating a powersupply that also applies the electrical potential to the at least onecorona electrode.
 63. The method for applying an electric field or anelectrical potential to a combustion reaction of claim 61, whereinapplying an electrical potential condition to the burner includesholding the burner substantially at ground potential.
 64. The method forapplying an electric field or an electrical potential to a combustionreaction of claim 61, wherein applying an electrical potential conditionto the burner includes galvanically isolating the burner from ground andfrom voltage sources such that the burner is electrically floating. 65.A burner system, comprising: a burner configured to support a flame in aflame position; and a first electrode having a sharp tip, the firstelectrode being positioned, relative to the burner, such that the sharptip of the first electrode is oriented toward the flame position, at adistance that is sufficient to prevent contact of the sharp tip with aflame supported by the burner.
 66. The system of claim 65 wherein thesharp tip is one of a plurality of sharp tips of the first electrode,each of the plurality of sharp tips being positioned along a first axis.67. The system of claim 66 wherein the sharp tips of the plurality ofsharp tips are arranged in a saw tooth pattern.
 68. The system of claim66 wherein the first electrode is positioned with the first axis lyingparallel to a central axis of the flame position.
 69. The system ofclaim 65 wherein the first electrode has a blade shape including alongitudinal taper to the sharp tip, which forms an edge of the bladeshape.
 70. (canceled)
 71. The system of claim 65 wherein the firstelectrode is supported by a structure configured to vary the position ofthe first electrode, relative to the flame position. 72.-74. (canceled)75. The system of claim 65, comprising a voltage source electricallycoupled to the electrode and configured to apply to the first electrodea voltage having a magnitude sufficient to cause the first electrode toproduce a corona discharge from the sharp tip.
 76. The system of claim75, comprising a second electrode electrically coupled to the voltagesource and positioned, relative to the first electrode and burner, suchthat a portion of the charged particles ejected by the first electrodetoward the second electrode impinge on the flame position. 77.-79.(canceled)
 80. The system of claim 75, comprising a second electrodecoupled to the voltage source, the second electrode being positioned andconfigured to apply a counter charge to a fluid stream ejected by theburner.
 81. (canceled)
 82. The system of claim 80 wherein the secondelectrode has a toroidal shape and is positioned, relative to theburner, such that the fluid stream passes substantially along a centralaxis of the toroidal shaped second electrode.
 83. The system of claim 82wherein the second electrode is positioned to act as a flame anchor to aflame supported by the burner.
 84. The system of claim 80 wherein thesecond electrode is outside the flame position.
 85. The system of claim65, comprising an electrode shield positioned between at least a portionof the first electrode, including the sharp tip, and the flame position,and configured to block transmission of radiant heat.
 86. The system ofclaim 65 wherein the sharp tip is one of a plurality of sharp tips ofthe first electrode, the system further comprising an electrode shieldshaped and positioned between each of the plurality of sharp tips of thefirst electrode and the flame position, and configured to blocktransmission of radiant heat. 87.-98. (canceled)
 99. The method forapplying an electric field or voltage to a combustion reaction of claim34, comprising ablating the sharp tip of the discharge electrode,including ablating a core and an outer layer of the discharge electrodeat respective rates that maintains a portion of the core extending asthe sharp tip from the outer layer.
 100. The method for applying anelectric field or voltage to a combustion reaction of claim 99,comprising maintaining a selected distance between the sharp tip and theflame by extending the discharge electrode at a rate that issubstantially equal to a rate of ablation of the discharge electrode.101. A device, comprising: a first electrode having a sharp tip at afirst end of the first electrode; and an electrode shield electricallyand mechanically coupled to the electrode in a position on alongitudinal axis of the sharp tip and spaced a distance from the sharptip. 102.-103. (canceled)